The ability to conduct high-speed data communications between relatively remote data processing systems and associated subsystems is currently a principal requirement of a variety of industries and applications, such as business, educational, medical, financial and personal computer uses. Moreover, it can be expected that present and future applications of such communications will continue to engender more such systems and services. One technology that has attracted particular interest in the telecommunication community is digital subscriber line (DSL) service. DSL technology enables a public service telephone network (PSTN) to use existing telephone copper wiring infrastructure to deliver a relatively high data bandwidth digital communication service, that is selected in accordance with expected data transmission rate, the type and length of data transport medium, and schemes for encoding and decoding data.
FIG. 1 is a reduced complexity diagram of the general architecture of a DSL system, having a pair of mutually compatible digital communication transceivers 1 and 3 installed at remotely separated ‘west’ and ‘east’ sites 2 and 4, respectively, and coupled to a communication link 10, such as a twisted pair of an existing copper plant. One of these transceivers, for example, the west site transceiver 1, may be installed in a digital subscriber line access multiplexer (DSLAM) 6 of a network controller site (such as a telephone company central office (CO)). The DSLAM is coupled with an associated network backbone 5 that provides access to a number of information sources 7 and the Internet 8. As such, the west site transceiver 1 is used for the transport of digital communication signals, such as asynchronous transfer mode (ATM)-based packetized voice and data, from the west central office site 2 over the communication link 10 to an integrated access device (IAD), which serves as the DSL transceiver 3 at the east end of the link, and may be coupled with a computer 9 at a customer premises, such as a home or office.
For transporting data and voice, a network of the type shown in FIG. 1 may employ ATM Adaptation Layer 5 (AAL5) for data transport, and AAL2 for voice transport. As ATM is a ‘cell’-based asynchronous transfer protocol, the digitally encoded voice samples must be packaged into properly formatted streams that incorporate correct header and packet or cell processing information, to ensure a continuous flow of voice and voice-band data cells across the ATM fabric. This requires that a prescribed number of digitally encoded voice samples be treated as a unit; the unit is processed in accordance with the appropriate protocol algorithms to produce associated auxiliary encapsulating components for the voice packet. These auxiliary components include headers, checksums, and the like, that are inserted into the data stream at the correct location (e.g., prepended headers, appended checksums) to realize a completely formatted packet stream, such as that shown in the reduced complexity example of FIG. 2.
Because the auxiliary components are derived from the digitally encoded voice samples, which can arrive at any time and have priority over data, it is necessary to buffer the voice samples and then perform the necessary processing to produce the proper auxiliary components that are to be prepended or appended to the digitally encoded voice sample data field to realize a ready for transmission packet, such as a fifty-three byte ATM cell.
One relatively straightforward approach to generating the overhead components would be to have the host processor pull all the voice samples one at a time from the communication coprocessor and then copy them from one buffer location to another, as it iteratively produces each auxiliary byte and assembles and restores these bytes along with the voice samples into successively larger groups, until the desired composite cell structure is eventually realized. Unfortunately, this unduly burdens the host processor and increases the latency of the system.